Abstract
Using a data sample of $448.1\times10^6$ $\psi(3686)$ events collected at $\sqrt{s}=$ 3.686 GeV with the BESIII detector at the BEPCII, we search for the rare decay $J/\psi \to \phi e^+ e^-$ via $\psi(3686) \to \pi^+\pi^- J/\psi $. No signal events are observed and the upper limit on the branching fraction is set to be $\mathcal{B}(J/\psi \to \phi e^+ e^-) < 1.2 \times 10^{-7}$ at the 90\% confidence level, which is still about one order of magnitude higher than the Standard Model prediction.
Highlights
which may be sensitive to new physics
mainly through the three dynamic processes shown in Figs
the EM process proceeding through three virtual photons
Summary
The BESIII experiment has accumulated 4.48 × 108 ψð3686Þ events which is the largest ψð3686Þ data sample produced directly in eþe− annihilation in the world. By tagging the two soft pions in the decay of ψð3686Þ → πþπ−J=ψ, the final states from J=ψ decay can be well distinguished This provides an almost backgroundfree sample to investigate the rare J=ψ decay, which may be sensitive to new physics. The rare decay J=ψ → φeþe− is one particulary interesting example [1] If a positive result were obtained with a branching fraction in the expected range, this decay channel could be used to extract information of some interesting mesons such as f0ð980Þ or a0ð980Þ since their form factors are involved in the predictions. BESIII has available the currently world’s largest data sample of directly produced J=ψ, this is not. We report on search for the rare decay of J=ψ → φeþe− via ψð3686Þ → πþπ−J=ψ
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